From Ozone Success, a Potential Climate Model

In 1985, scientists studying the air over Antarctica stumbled on a gaping breach in the billion-year-old atmospheric radiation shield that makes Earth’s surface habitable.

The discovery of a seasonal “hole” in this veil of ozone molecules was so unexpected — “the surprise of the century,” one chemist later called it — that it was presumed to be a data glitch.

It wasn’t. Soon other experts found a connection between the ozone hole and the use of chlorofluorocarbons, or CFCs, and similar synthetic chemicals in solvents, refrigeration, sprays and the like.

The chemical threat to the ozone layer had been identified in 1974, and industries and governments were planning to shift to safer substitutes. But it took the ozone hole, glaring from satellite images like a purple bruise, to make eliminating such chemicals a global imperative. On Sept. 16, 1987, an initial batch of countries signed the Montreal Protocol, a treaty that has since grown and led to bans on 95 percent of the ozone-eating compounds.

On Sunday, diplomats, scientists and environmentalists gathered in Montreal to celebrate the 20th anniversary of the treaty and to spend a week discussing possible new steps to speed an end to remaining ozone threats.

Many are using the anniversary to bolster the idea that a similar success can be achieved with carbon dioxide and other heat-trapping greenhouse gases linked to global warming (including some of the ozone-destroying chemicals and some of the replacements for them). Fresh international climate talks begin at the United Nations on Monday and at a meeting in Washington organized by the White House late next week. Some veterans of both the ozone and climate fights insist that the Montreal success is a model for climate action.

“The lesson from Montreal is that curbing global warming will not be as hard as it looks,” said David D. Doniger, an early campaigner against ozone-damaging chemicals for the Natural Resources Defense Council who now directs the group’s climate work.

But many experts on the circumstances — scientific, diplomatic and economic — surrounding the 1987 treaty signing say that while some things are similar now, like the looming environmental risks revealed by evolving science, almost everything else is very different.

Ozone molecules, tenuous trios of oxygen atoms, serve as a planetary sun block of sorts, limiting the bombardment of the Earth’s surface by ultraviolet radiation that can cause skin cancers and cataracts, and harm some plants and animals.

When F. Sherwood Rowland and Mario J. Molina first posited in 1974 that CFCs and similar chemicals could waft to the stratosphere and break up ozone, the threat quickly captured public attention.

In 1977, long before the climate disaster movie “The Day After Tomorrow,” Hollywood released “Day of the Animals,” in which ozone destruction caused wildlife to run amok.

But it was cancer that really brought the issue home, said Susan Solomon, a senior scientist with the National Oceanic and Atmospheric Administration who in 1986 led work linking CFCs and related chemicals to polar ozone losses. “Skin cancer is deeply personal, and virtually every person on the planet has either known someone who has had cancer or had it themselves,” Dr. Solomon said.

Photo

Satellite instruments monitoring the ozone layer are used to create images depicting ozone over Earth. The blue and purple show where there is the least amount of ozone; the green, yellow and red show where there is more.Credit
NASA

The risks from global warming are far different, said Dr. Solomon, who was the co-leader of the latest scientific report by the Intergovernmental Panel on Climate Change. “It is much less personal for most people, except perhaps if you’re in places like Vanuatu,” she said, referring to one of several low-lying island nations threatened by rising seas. “It’s mostly beyond our generation.”

In the 1980s, despite persistent scientific uncertainties over the threat to the ozone layer, action to move away from ozone-damaging chemicals was swift, largely because there was little cost involved and alternatives were developed as the need arose, experts said.

To preserve the ozone shield, the United States, joined soon by Canada and Scandinavian countries, banned “nonessential” uses of CFCs — hair sprays, for example — in 1978, just three years after the theory was first described in the journal Nature.

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The Natural Resources Defense Council, seizing on an opening left by a proposed rule to limit CFCs that was written in the last days of the Carter administration, filed a lawsuit in 1984 that prompted the Environmental Protection Agency to seek broader bans. The domestic action helped set the stage for treaty talks.

“That N.R.D.C. suit was critical because it turned the burden of proof around from having to show there was a problem to proving there was not,” said Roger A. Pielke Jr., a political scientist at the University of Colorado, Boulder.

Still, $135 billion worth of air conditioners and other equipment in the United States, and billions more around the world, relied on the old chemicals, and the science remained murky. So DuPont and other companies waited to seek alternatives, according to company scientists.

In 1985, the murk cleared somewhat. An international scientific assessment of CFCs and ozone created a near-worldwide consensus that the risks of allowing the long-lived chemicals to keep building in the atmosphere were unacceptable.

DuPont, while gaining less than 2 percent of its revenues from such compounds, saw a need to find substitutes and the prospect of new markets, and began a $500 million research effort that spawned a suite of alternatives.

With global warming, in contrast, economists and climate experts say it will take billions of dollars a year in basic research, sustained over many years, to even have a chance of finding energy sources that can compete with fossil fuels but produce no greenhouse gases.

In addition, the ozone treaty gave developing countries a decade-long grace period on CFC phaseouts and compensated them for the cost of shifting to safer chemicals. Talks over strengthening climate agreements have stumbled repeatedly over efforts to get concrete commitments on emissions cuts from the United States, and the involvement of developing countries, particularly giants like China.

The final momentum for the Montreal treaty was provided by the discovery of the ozone hole, which served as kind of wake-up call, for the first time bringing home the realization that humans could have a direct effect on the planet’s future.

Environmental campaigners have for years been seeking a comparable icon for climate change, be it drowning polar bears, Hurricane Katrina or the deadly European heat wave of 2003. But the incremental nature of the threat posed by building greenhouse gases is for many still trumped by concerns like Iraq and health care.

Mack McFarland, the chief atmospheric scientist for DuPont, said the surprise appearance of the ozone hole should serve as a warning to anyone waiting for stronger evidence of danger before acting to cut emissions of greenhouse gases.

“The science of ozone is so simple compared to the global climate system,” Dr. McFarland said. Referring to the discovery of the polar hole, he added: “If we missed something so fundamental with ozone, what are we missing with the climate system? Admittedly, it can go either way. But do we want to take that chance?”

Correction: September 19, 2007

An article in Science Times yesterday about the 1987 Montreal treaty to curb ozone-destroying chemicals misspelled the surname of the chief atmospheric scientist for DuPont. He is Mack McFarland, not MacFarland.

A version of this article appears in print on , on Page F2 of the New York edition with the headline: From Ozone Success, a Potential Climate Model. Order Reprints|Today's Paper|Subscribe